1. Field of the Invention
The present invention relates to systems and methods of providing mobile cellular communications, and in particular, to a method and system for Internet services in a mobile cellular communications network.
2. Description of the Related Art
Traditionally, cellular mobile and wireless communication systems have been designed and built for voice service. With the explosive growth of Internet applications and users, there is an increasing demand on providing Internet service to mobile users based on the existing cellular systems. Voice communication is characterized as connection-oriented, circuit-switching, constant bit-rate, and low tolerance to loss and jitter. In contrast, Internet service is characterized by connectionless communication, packet-switching, bursty traffic patterns, multicast, differentiation of multiple classes of services, and often, best effort and loss-tolerant communication. In addition, some Internet applications desire much higher and often on-demand bandwidth such as videoconferencing using variable-bit-rate coding. Thus far, the development of a cost effective network architecture and necessary system components to meet these different requirements of Internet service on top of the existing infrastructure of voice-oriented cellular networks has remained an elusive goal.
FIG. 1 is a depiction of a PACS (Personal Access Communication System) 100. The PACS is an emerging low-tier, low-cost PCS standard for cellular wireless services in densely populated areas. The PACS standard defines two data communication modes (circuit-mode and packet-mode).
In a PACS network 100, users obtain services through subscriber unit (SU) devices 102. SUs 102 communicate with radio ports (RPs) through a time division multiple access (TDMA) uplink and time division multiplexing (TDM) downlink. The influence of the RPs 104, as determined by their transmission and reception range and that of the SUs 102, define cells 112.
Nearby RPs 104 are controlled by a radio port control unit (RPCU) 106, which concentrates all traffic from the RPs 104 and connects it to a backbone voice or data network. User authorization and other related functions are provided by an access manager (AM) 108 and a signaling network 110.
The PACS standard packet-mode data service serves as the fundamental building block for implementing and managing IP services in the Internet service architecture of the present invention.
The packet-mode data service of PACS, known as PACS Packet Channel (PPC), provides the user with a variable bandwidth, asynchronous, bandwidth-on-demand, and asymmetric data service at data rates up to 256 thousand bytes per second (Kbps). It is based on frequency-division-duplex, TDMA uplink and TDM downlink PACS physical interface which is common to both circuit-mode and packet-mode services. Uplink refers to the direction from SU 102 to RPCU 106, and downlink is from RPCU 106 to SU 102. The high data rate and variable bandwidth nature of PPC is well suited to multimedia and the bursty nature of Internet traffic. PPC supports dynamic sharing of bandwidth with the PACS circuit mode services (voice, circuit-mode data, etc.), allowing PPC to utilize the bandwidth otherwise idle.
FIG. 2A is a diagram presenting a depiction of PPC layers. The PPC consists of three layers: a PACS physical layer 202, datalink layer (DL) 204 and security layer (SL) 206. The PACS physical layer performs coding of TDMA uplink and TDM downlink. Both uplink TDMA and downlink TDM frames are 2.5 msec long. Each frame consists of 8 slots and each slot is 10 bytes long. The task of the PPC DL layer 204 is to provide a reliable and connectionless communication service to the SL layer 206, which includes medium access control (MAC), fragmentation and segmentation, and error detection and correction. The major functions of SL layer 206 include handset registration, user authentication, and data encryption.
FIG. 2B illustrates the PACS standard encapsulation and framing procedure. First, the PPC copies each network layer packet 210 in an SL packet 212 with a header 214 and checksum 216 with optional payload encryption to prevent eavesdropping over the air. It then encapsulates each SL packet 212 in a DL packet 218 with proper header 220 and checksum 222. Each DL packet 218 is divided into one or more DL fragments 224 and finally each DL fragment 224 is subdivided into DL segments 226. Fragmentation is for the high-level medium access function—the PPC must assign a slot number (out from the 8 slots) for each DL fragment 224, and all segments of a fragment 224 must be transmitted in the same slot. Segmentation is to fit the TDM/TDMA airlink structure, which is depicted in FIG. 2C.
For downlink fragmentation, the maximum fragment size is 576 bytes of data. A larger packet must be fragmented but each fragment can be transmitted in different slots in parallel. Uplink fragments may be 256 segments long, therefore all uplink DL packets 218 are sent in a single fragment.
FIGS. 2D and FIG. 2E are diagrams depicting the encapsulation uplink and downlink messages in greater detail.
FIG. 3 is a diagram of the functional architecture of the PPC. A contention function (CF) 302 performs the small subset of DL medium access and acknowledgment procedures that are highly time critical. A packet data controller unit (PDCU) 304 handles the rest of the DL and SL functions. The CF 302 resides in the RP 104, and PDCU 304 is typically implemented in the RPCU 304.
Each packet-mode SU 102 has a subscriber identity (SubID). The SubID is only used to authenticate a user during registration. In addition, each active SU 102 also has a transient identifier called LPTID (Local Packet Terminal Identifier). The LPTID is a one-byte integer specifying the source/destination SU 102 in every uplink/downlink slot over the wireless link. Each time an SU 102 enters a cell 112 (by cold-start or roaming), it is assigned a unique LPTID for as long as it remains in the cell 112. An LPTID is only valid in the current cell 112 and an SU 102 can have a different LPTID value in a different cell 112. LPTIDs are assigned by the PACS network 100 after successful registration and re-assigned after each hand-off. When the SU 102 moves to an adjacent cell, the old LPTID will not be used any more, and a new LPTID must be allocated in the new cell 112. The LPTID is thus transient in nature. Table I below shows the current allocation scheme for LPTID as defined in the standard.
TABLE ILPTID ValuePurpose0x00Null0x01Registration message (used before the SU 102 isassigned an LPTID).0x02-0xEFAssigned to SUs 102 upon registration and handoff.This allows up to 238 SUs 102 in each cell 112.0xF0-0xFDReserved for future use0xFESystem information (used to broadcast datalink layer,network layer, and “system information channel”parameters).0xFFAll SUs 102. (Used for messages that must bebroadcast to all SUs 102.)
After successful registration, each active SU 102 is assigned a datalink layer address for use in the current cell 112. The datalink layer address is a one-byte integer called LPTID (Local Packet Terminal ID).
Whenever a SU 102 enters the network, it performs a PPC registration. Two major tasks of PPC registration are authentication and LPTID assignment. At the beginning of the registration, the SU 102 sends a registration request message (PACKET_REG_REQ) which includes its SubID (assuming no user anonymity). The AM 108 then authenticates the SU 102 using this SubID. Once the authentication is successful, the PDCU 304 assigns a new LPTID and sends the registration acknowledgment message (PACKET_REG_ACK) with this LPTID back to the SU 102. From then on, the SU 102 identifies data destined for it by the LPTID until it de-registers from the network or moves to a different cell 112.
A cell hand-off is known as an automatic link transfer (ALT). ALT takes place when SU 102 is crossing the wireless cell 112 boundary. It begins when an SU 102 detects the degradation of the present physical channel and finds another physical channel with sufficiently high quality. The SU 102 then sends an ALT request message to the new RP 102. Once the request is accepted, the SU 102 gets an ALT execution message back and a new LPTID for the new cell 112. Depending on whether the two channels are associated with the same RPCU 106 or not, ALT can be divided into two categories: intra-RPCU ALT when SU 102 moves to an adjacent cell in the same RPCU 106, and inter-RPCU ALT when SU 102 moves to a different RPCU 106.
Thus far, PACS 100 has been developed primarily as a voice network. Although the standard does define two data communication modes (circuit-mode and packet-mode), Internet service support in a PACS network 100 has not been addressed. Internet access could be provided through the circuit-mode data service, where users establish a point-to-point protocol (PPP) connection to an Internet Service provider (ISP) over a dedicated PACS channel. But, because of the fixed bandwidth, this type of access is unscalable and inefficient for Internet applications.
What is needed is a network architecture and a set of design guidelines for achieving seamless integration of cellular networks with the global Internet by supporting mobile and multicast IP services in cellular networks. The present invention satisfies that need.